Controlling the free volume of type III porous liquids by tailoring solvent for enhanced CO2 capture

Abstract

Porous liquids (PLs) are an emerging class of liquid materials that combine the porosity of solids with the fluidity of liquids, showing great potential in carbon dioxide (CO₂) capture. Meanwhile, understanding the factors that govern CO₂ absorption is critical to the development of high-capacity PLs. Based on this, we report two novel 1,8-diazabicyclo[7.7.2]dec-7-ene (DBU) based PLs by incorporating the ZIF-8 porous framework into two ionic liquids (ILs) – DBU-2-methylimidazole ([DBUH][2-MeIm], IL1) and DBU-acetic acid ([DBUH][AC], IL2). Their physicochemical properties and CO₂ absorption mechanisms are studied by combining spectroscopic investigations and simulation calculations. The research objective is to create a fundamental understanding of how ILs enable PLs formation and shows higher efficiency for CO₂ capture. The results show that ZIF-8 can be uniformly dispersed in IL1 through non-covalent interactions. The formed PL1 has better fluidity, containing greater free volumes for CO₂ transmission and storage as well as more efficient absorption active sites, which endow PL1 with excellent CO₂ absorption capacity. The CO₂ absorption of PL1 is a combination of physical adsorption through van der Waals interaction and reversible chemical absorption. Moreover, the synergistic effect between the absorption active sites of PLs and the nano-confined spaces of the interface between ILs and ZIF-8 in PLs is identified as a powerful internal driving force for the improvement of CO₂ absorption capacity. This work will pave the way for the rational design of novel PLs for industrial CO₂ capture.